In order to determine the optimum technological conditions of the seed koji machine for preparing the seed koji, Aspergillus oryzae 3.951 was used, and the spore number was used as the quality evaluation index of the seed koji to study the relationship between the culture condition and the quality of the seed koji. The results of single factor and orthogonal test showed that the air volume had the greatest influence on the quality of the seed koji, followed by the amount of hydration water and the amount of yeast extract, and the amount of water infiltration was relatively small. The optimum conditions for cultivating the seed koji using the 100 kg seed koji machine are: water content 110%, air volume 2 m3/h, water replenishment 70 L/can, and yeast extract 2.5%. Under the optimized condition, the number of spores of the seed koji can reach 10 billion / g (dry basis) or more, and the quality of the brewed soy sauce is obviously improved